Heavy atom quenched coumarin probes for sensitive and selective detection of biothiols in living cells

A series of turn-on fluorescent probes with halogen acetyl amide at the 3-position of coumarin derivatives were synthesized. Fluorescence of these probes was efficiently quenched by heavy halogen atoms (Br and I, not Cl), which could be successfully used for selective detection of biothiols with the sensitivity of Cys > GSH > Hcy and much higher than thiol containing proteins. These represent the smallest fluorescence quenchers in designing fluorescent probes for detecting both endogenous and exogenous biothiols in living cells.